= Solution
The <Hammett equation> is $\log(k_X/k_H)=\rho\sigma_X$. The positive slope, $\rho=+1.97$, means electron-withdrawing para substituents accelerate hydrolysis. They increase <carbonyl> electrophilicity and stabilize the additional negative charge associated with the addition transition state/<tetrahedral intermediate>. Strong electron donation has the opposite effect. <Hydroxide> addition to the acyl carbon, followed by tetrahedral-intermediate collapse and aryloxide loss, is consistent with both this trend and the bimolecular rate law.
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